Method for converting micro- to nano-crystalline cellulose

ABSTRACT

The invention is directed to a simple and economical method for producing nanocrystalline cellulose from microcrystalline cellulose by contacting frozen concentrated sulfuric acid with microcrystalline cellulose, diluting the mixture in water and hair-shaped ice to hydrolyze the microcrystalline cellulose, and separating the NCC. Another aspect of the invention pertains to an apparatus for conducting this method which includes an acid resistant hydrolysis container having a cooling jacket containing a hollow stirrer each of which may be filled with liquid nitrogen.

BACKGROUND Field of the Invention

The invention pertains to wood technology and wood chemistry and toproduction of nanocrystalline cellulose.

Description of Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventor(s), to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Cellulose is the most abundant polymer on the Earth and is produced bymembers of the plant kingdom. It is composed of cellulose microfibrilswhich contain amorphous and crystallized regions. See Hindi, S. S. Z.2017b. Suitability of date palm leaflets for sulfated cellulosenanocrystals synthesis. Nanoscience and Nanotechnology Research, 2017,Vol. 4, No. 1, 7-16. DOI:10.12691/nnr-4-1-2, incorporated herein byreference in its entirety.

Microcrystalline cellulose (“MCC”) is produced by dissolving theamorphous regions of the cellulose microfibrils which liberates thecrystalline regions and produces microcrystalline cellulose (MCC) ornanocrystalline cellulose (NCC). See Hindi, S. S. Z. 2017b, id.; Hindi,S. S. Z. 2017c. Nanocrystalline Cellulose: Synthesis from Pruning Wasteof Zizyphus spina christi and Characterization. Nanoscience andNanotechnology Research. 4(3):106-114. doi: 10.12691/nnr-4-3-4; andHindi, S. S. Z. 2017d. Microcrystalline cellulose: The inexhaustibletreasure for pharmaceutical industry. Nanoscience and NanotechnologyResearch. 4 (1): 22-31; or Hindi, S. S., Albureikan, M. O., Al-Ghamdy,A. A., Alhummiany, H. and Ansari, M. S. 2017. Synthesis andcharacterization of gum Arabic based bio plastic membranes. Nanoscienceand Nanotechnology Research, 4 (1): 32-42. DOI:10.12691/nnr-4-1-3; eachincorporated herein by reference in its entirety. Alpha-cellulose is oneof three classes of cellulose and has a high degree of polymerizationand stability.

Conventionally, different processes such as reactive extrusion, enzymemediated, steam explosion and acid hydrolysis, are used to produce MCC.Acid hydrolysis is favored and can be performed using mineral acids suchas HCl, HBr, and H₂SO₄, or various ionic liquids. Usually 2.0-2.5 N HClis used as the hydrolyzing agent for MCC production; Hindi, 2017d, id.

MCC is an important additive in the pharmaceutical, food, cosmetic, oildrilling, and plastic industries. In the pharmaceutical industry, it isan important tableting excipient due to its superior binding propertiesand ability to be directly compressed into tablets; Hindi, 2017d, id.

Like MCC, NCC can be synthesized via acid hydrolysis by using HCl, HBror H₂SO₄. For example, treatment of α-cellulose with moderatelyconcentrated sulfuric acid (64% w/w) for about two hours yields about 30wt % NCC. The NCC produced has a short length ranging from 200-400 nmand a width less than 10 nm; Beck-Candanedo et al., 2005; Hindi. 2017;Araki, J., Wada, M., Kuga, S. Okano, T. Low properties ofmicrocrystalline cellulose suspension prepared by acid treatment ofnative cellulose. Colloids Surf. A 1998, 142, 75-82; Beck-Candanedo, S.,Roman, M., and Gray, D. G. 2005. Effect of reaction conditions on theproperties and behavior of wood cellulose nanocrystal.Biomacromolecules. 6 (2):1048-54; and Hindi, S. S. Z. 2017b, eachincorporated herein by reference in their entirety.

Hydrolysis with acids like HCl or HBr does not substantially affect thesurface charge and sulfur content of the NCC. For example, acidhydrolysis using HCl produces NCC with minimum surface charge. However,it has been found that sulfuric acid provides more stable aqueoussuspensions of NCC than hydrochloric acid (Araki et al., 1998, id.).Acid hydrolysis with H₂SO₄ leads to a negatively charged surface, due tothe esterification of surface hydroxyl groups to give charged sulfategroups; see Dong, X. M., Revol, J. F., Gray, D. 1998. Effect ofmicrocrystalline preparation conditions on the formation of colloidcrystals of cellulose. Cellulose. 5: 19-32, and Beck-Candanedo et al.,2005, each incorporated herein by reference in their entirety.

In many conventional NCC production schemes, NCC is synthesized by acidhydrolysis of previously wetted α-cellulose precursor, such as woodpulp, using moderately concentrated H₂SO₄ (e.g., 64% wt/wt) and waterice for cooling. In one example of such a conventional processhydrolysis proceeds for about 60 minutes at a hydrolysis temperaturebetween 45° and 70° C. After hydrolysis, the hydrolyzed precursorsolution is quenched overnight by a large volume of distilled water—suchas 10-times the volume of the hydrolysis solution—and then decanted.After that, it is centrifuged at 1,500 rpm and a solid, precipitatedfraction containing fractured fibers is discarded. Subsequently, thecollected supernatant solution is recentrifuged via five centrifugationcycles at 14,000 rpm to recover NCC which is then washed untilneutralization. When the H₂SO₄ concentration is diluted to about 0.5 wt%, colloidal NCC appears.

To remove the H₂SO₄ residues from colloidal NCC, dialysis is performedwith a concentration of 1 wt % NCC for about one week against deionizedwater. After that, ultrasonic treatment is applied at 0° C. for 30minutes. Then, centrifugation is done at 14,000 rpm for about 45minutes.

The resulting yield of NCC was found to range between 8-30%. See Habibi,Y., Lucia, L. A., and Rojas, O. J. 2010. Cellulose Nanocrystals:Chemistry, Self-Assembly, and Applications. Chem. Rev. 2010, 110,3479-3500; Kumar, A., Negi, Y. S., Choudhary, V. and Bhardwaj, N. K.2014. Characterization of cellulose nanocrystals produced byacid-hydrolysis from sugarcane bagasse as agro-waste. Journal ofMaterials Physics and Chemistry, 2 (1): 1-8. doi: 10.12691/jmpc-2-1-1;and Hindi, S. S. Z. 2017a. Some Crystallographic Properties of CelluloseI as affected by cellulosic resource, smoothing and compution methods,International Journal of Innovative Research in Science, Engineering andTechnology (IJIRSET). 6 (1): 732-752. DOI:10.15680/IJIRSET.2017.061127;and Hindi, S. S. Z. 2017b, each incorporated herein by reference intheir entirety.

Other processes using moderately concentrated sulfuric acid are known,such as that described by Ioelovich, ISRN Chem. Eng. Volume 2012 (2012),Article ID 428974, 7 pages at http://_dx.doi.org/10.5402/2012/428974,which describes a process using 50-65% sulfuric acid to treat MCC.However, only regenerated cellulose having a non-natural polymorph(cellulose II) was obtained by this process by using a concentration of65% sulfuric acid.

Most global synthesis schemes for NCC use wood pulp as a cellulosicprecursor and not MCC. Benefits of using microcrystalline cellulose(MCC) as a starting material instead of cellulosic fibers for synthesisof nanocrystalline cellulose (NCC), for example but not limited to thefollowing items: (i) production of a NCC unity is attained while usingless cellulosic precursor; (ii) the method consumes less concentratedH₂SO₄; (iii) MCC can be produced as a fine powder that is easy to handlewithin the synthesis apparatus rather than in a fibrous form oftraditional cellulose; and MCC is more resistant to concentrated H₂SO₄compared to α-cellulose, thus compared to cellulosic fiber the treatmentof MCC with acid is less susceptible to degradation.

Other limitations of conventional NCC production processes include therequirement for use of expensive machinery, such as sonication baths,sonication props, centrifuges, dryers, lyophilizers and spray-driers ora complicated series of process steps such as requirements forcentrifugation, sonication, neutralization, dialysis, and/or subsequentdrying of an NCC product. Consequently, there is a need for a lesscomplicated process that produces NCC in less time and at a lower cost.

In view of the limitations and drawbacks to conventional means forproducing NCC, the inventors sought to develop and developed a simple,fast, convenient, industrially-scalable, and lower cost way ofmanufacturing NCC.

BRIEF SUMMARY OF THE INVENTION

One non-limiting aspect of the invention is method for producingnanocrystalline cellulose (“NCC”) from a precursor that containsmicrocrystalline cellulose (“MCC”) by fragmenting MCC and liberatingnanocrystalline cellulose. Hydrolytic fragmentation of MCC occurs in thepresence of frozen concentrated sulfuric acid (98.06%) which form apaste in combination with the MCC substrate. Flash hydrolysis is carriedout in a narrow low temperature range for a short period of time bysudden dilution of the paste with a mixture of cold water andhair-shaped ice forming a turbid solution. NCC is recovered from theturbid solution, washed and neutralized, and optionally dried. It is notnecessary to use equipment such as a centrifuge to recover the NCC as itmay be simply recovered using inexpensive filter paper or a Goochcrucible.

These and other features of the invention will become readily apparentupon further review of the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A describes the production of nanocrystalline cellulose frommicrocrystalline cellulose by icy H₂SO₄-hydrolysis.

FIG. 1B is a photo of crude paste containing NCC formed by treatment ofMCC with concentration sulfuring acid.

FIG. 1C depicts a vacuum filtration system with continuous cooling.

FIG. 1D shows precipitated NCC ready to be filtered using Whatman paperno. 44.

FIG. 1E shows oven-dried NCC powder produced from the filtrate.

FIG. 2A shows an optical image of urchin shaped NCC produced as a finalcrystal growth architecture.

FIG. 2B. Large NCC urchins produced by hot hydrolysis.

FIG. 2C. Medium NCC urchins produced by hair-ice cold hydrolysis.

FIG. 2D. Dwarf NCC urchins produced by cryogenic-cold hydrolysis.

FIG. 3A shows a SEM micrographic image of the NCC backbone of NCC(35,000×).

FIG. 3B depicts flower shaped aggregates of NCC (10,000×).

FIG. 3C. shows a SEM micrograph of rod-shaped NCC.

FIG. 3D depicts a SEM micrograph of a stratified agglomeration of NCC.

FIG. 4 depicts a TEM micrograph of NCC clusters having various shapes.

FIG. 5 depicts a X-ray diffractogram of the NCC synthesized as disclosedherein. Boxed values left to right: 18.29°, 19.26° and 21.13°.

FIG. 6 shows Fourier Transform Infrared (FTIR) spectra of the NCCproduced as disclosed herein. Indicated values from left to right: 3439,2922, 2853, 1737, 1636, 1468 and 1109.

FIG. 7 shows thermogravimetric analysis (TGA) diagram of NCC synthesizedaccording to the method of the invention showing from left to right,mass changes of −0.69 mg, −3.61 mg, −3.65 mg, and −1.72 mg. Y axis scalefrom 6.0 to 16.5. X axis scale from 20 to 520. Mass change from left toright: −0.69, −3.61, −3.65, and −1.72 mg.

FIG. 8. Shows a differential thermal analysis (DTA) of NCC synthesizedas disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

The invention employs MCC as a starting material or substrate for NCCproduction. The inventors have found that this confers several benefitscompared methods that use other cellulosic substrates. These benefitsinclude production of NCC unity using less cellulosic precursor,consumption of less sulfuric acid, a reduced risk of MCC substratedegradation by acid compared to other cellulosic substrates, and easierhandling, standardization, and machine processing of a MCC cellulosicsubstrate in apparatus used to hydrolyze and recover a NCC product.

Microcrystalline cellulose or MCC is composed of glucose units connectedby 1-4 beta glycosidic bonds. These linear cellulose chains are bundledtogether as microfibrils spiraled together in the walls of plant cells.Each microfibril can exhibit a high degree of three-dimensional internalbonding resulting in a crystalline structure that is insoluble in waterand resistant to reagents. There are, however, relatively weak segmentsof the microfibril with weaker internal bonding. These are calledamorphous regions because of the single-phase structure of microfibrils.The crystalline region is isolated to produce microcrystallinecellulose. The MCC can be synthesized by different processes such asreactive extrusion, enzyme mediated, steam explosion and acidhydrolysis. The later process can be done using mineral acids such asHCl, HBr or H₂SO₄ as well as ionic liquids. The role of these reagentsis to destroy the amorphous regions and retain the crystalline domains.The degree of polymerization of MCC is typically less than 400, such as125, 150, 175, 200, 250, 300, 350, <400 or 400 (or any intermediatevalue within this range). MCC and NCC may include those containing orobtained from chemically modified celluloses, such as cellulosecontaining sulfate groups.

Alpha-cellulose is one of three classes of cellulose and has a highdegree of polymerization and stability. Alpha cellulose has bothalternated regions, namely crystalline and amorphous regions extendedalong with microfibril axe; see Hindi, S. S. Z. 2017a. Microcrystallinecellulose: The inexhaustible treasure for pharmaceutical industry.Nanoscience and Nanotechnology Research. 4 (1): 22-31.10.12691/nnr-4-1-3; Hindi, S. S. Z. 2017b. Differentiation and SynonymsStandardization of Amorphous and Crystalline Cellulosic Products.Nanoscience and Nanotechnology Research. 2017; 4(3):73-85. doi:10.12691/nnr-4-3-1; Hindi, S. S. Z. 2017^(c) . Some Promising Hardwoodsfor Cellulose Production: I. Chemical and Anatomical Features.Nanoscience and Nanotechnology Research. 2017; 4(3):86-97. doi:10.12691/nnr-4-3-2; Hindi, S. S. Z. 2017^(d) . Suitability of date palmleaflets for sulphated cellulose nanocrystals synthesis. Nanoscience andNanotechnology Research, 2017, Vol. 4, No. 1, 7-16.DOI:10.12691/nnr-4-1-2; Hindi, S. S. Z. 2017^(e) . NanocrystallineCellulose: Synthesis from Pruning Waste of Zizyphus spina christi andCharacterization. Nanoscience and Nanotechnology Research. 2017;4(3):106-114. doi: 10.12691/nnr-4-3-4; and Hindi, S. S. Z. 2017^(f) .Some Crystallographic Properties of Cellulose I as Affected byCellulosic Resource, Smoothing, and Computation Methods. InternationalJournal of Innovative Research in Science, Engineering and Technology(IJIRSET). 6 (1): 732-752. DOI:10.15680/IJIRSET.2017.061127.

MCC substantially contains only the crystalline regions of thecellulosic microfibrils; see Hindi, S. S. Z. and Abohassan, R. A. 2016.Cellulosic microfibril and its embedding matrix within plant cell wall.International Journal of Innovative Research in Science, Engineering andTechnology 5 (3): 2727-2734; Hindi, S. S. Z. 2016^(a). Theinterconvertiblity of cellulose's allomorphs. International Journal ofInnovative Research in Science, Engineering and Technology (IJIRSET). 6(1): 715-722. DOI:10.15680/IJIRSET.2017.0601125. Hindi, S. S. Z. 2016b.Birefringence of bio-based liquid crystals. International Journal ofInnovative Research in Science, Engineering and Technology (IJIRSET). 6(1): 708-714. DOI:10.15680/IJIRSET.2017.0601124. As appreciated by theinventors, MCC is a homogeneous precursor for synthesis of NCC becauseit excludes amorphous regions due to its previous acid hydrolysis froman α-cellulose precursor. Other non-MCC precursors or special forms ofcellulose such as linter, starch, freeze-dried cellulose, lyophilizedcellulose, hemicellulose, unrefined alpha-celluloses or groundcellulosic fibers are not required.

Nanocrystalline cellulose or NCC describes cellulose particles, regions,or crystals that contain nanometer-sized domains. Dimensions of NCCdepend on the nature of the MCC precursor material, hydrolysis time,hydrolysis, temperature and on handling, such as on washing, filtrationand drying conditions.

In some embodiments, the nanocrystalline cellulose material ischaracterized by an average length-to-width aspect ratio of particlesfrom about 10 to about 1,000, such as about 15, 20, 25, 35, 50, 75, 100,150, 200, 250, 300, 400, or 500 (or any intermediate value within theseranges).

Nanofibrils are generally associated with higher aspect ratios thannanocrystals. Cellulose nanocrystals are typically rigid rod-shapedmonocrystalline cellulose domain (whisker) with 1, 5, 10, 20, 50, to 100nm (or any intermediate value within this range) in diameter and tens tohundreds, such as 10, 20, 50, 100, 200, 300, 400, 500, 600, 700, 800,900, 1,000 or >1,000 nanometers in length. Aspect ratios fornanocrystals are determined by dividing their lengths by theirdiameters. For example, nanocrystals having respective lengths of 100,200, 300, 400, or 500 nm and diameters of 4 nm have aspect ratios of 25to 125.

Nanofibrils may have a length of about 2,000 nm and diameter range of 5to 50 nm, translating to an aspect ratio of 40 to 400. In someembodiments, the aspect ratio is less than 50, less than 45, less than40, less than 35, less than 30, less than 25, less than 20, less than15, or less than 10.

The crystallinity index (CI) of the NCC made by the method of theinvention may range between 40, 50, 60, 70, 80, 90, 95, 96, 97, 98, 99,99.5, <100, or 100% (or any intermediate value within this range).Preferably, the CI of the NCC at least 85. The NCC made by the inventionmay exhibit an average crystallite size between about 1.8, 2.8, 3.8, or<5.0 or any intermediate value within this range. Lattice spacing in theNCC of the invention may fall within the range 0.19, 0.20, 0.21, 0.214,0.22, 0.23, 0.24, 0.25, or any intermediate value within this range.

Surprisingly, the inventors found that the method of the invention canfragment the MCC precursor into NCC that has normal nanometricproperties similar to those of cellulose I which is a form of celluloseexhibiting hydrogen-bonding found in natural cellulose. These fragmentsof MCC differ from regenerated cellulose II or chemically-treated formsof cellulose such as cellulose III or cellulose IV. In anotherembodiment the flash hydrolysis of the invention was found to graftthree sulfate groups onto the available carbon site numbers 3, 4, and 6of the glucopyranose unit constituting the cellulose chain.

Hydrolysis is cleavage of chemical bonds by the addition of water.Hydrolysis of amorphous regions of the MCC starting material isconducted under cooling conditions, such as at a temperature of 25, 20,15, 10, 5, or 0° C., preferably, hydrolysis occurs rapidly upon dilutionof a paste of concentrated sulfuric acid and MCC in a large volume ofwater and water ice crystals at a temperature within the range of 10-15°C. The mixture of MCC and concentrated sulfuric acid may be cooled usinga mixing and/or hydrolysis container or chamber that is equipped with ajacket holding liquid nitrogen and with a hollow stirrer filled withliquid nitrogen.

Dilution after contact and hydrolysis of the MCC starting material byconcentrated sulfuric acid under cooling conditions, of the hydrolyzedMCC (usually in the form of a paste) is carried out, preferably, veryrapidly, with water or with an aqueous buffer. Dilution may be performedunder cooling conditions and/or under an inert or reduced oxygenatmosphere to inhibit oxidation of NCC. It is not necessary to use otherliquids, such as ethanol or other alcohols, ethers, or liquid gases suchas liquid nitrogen, to make the paste or as components of a hydrolysismixture. It is not necessary to cool the substrate, paste or hydrolysismixture using liquid gases like liquid nitrogen or cooled gas vapors.

Filtration includes various ways of separating materials by filtrationsuch as those known in the art. A filter paper or other filter orfiltration device having a pore size in the range of 0.4, 0.5, 1, 1.5,2, 2.5, 3, ≥4 μm may be selected to recover the NCC. Different grades offilter paper may be selected depending on the size of the NCC particlesto be recovered, for example, Grade 602h filter paper has a pore size of2 μm and in a preferred embodiment, Whatman filter paper #44 type filterpaper (or its equivalent), which has a pore size of 3 μm, is used torecover NCC.

Gooch crucibles and fritted glass filters may also be used to recoverthe NCC, for example, a Gooch crucible may be fitted with a frittedglass filter having a fine pore size in the range of 0.4, 0.5, 1.0, 1.5,2, 2.5, 3, 3.5, and ≥4 μm and used to recover the NCC. Other modes offiltration are known and may be adapted to recover the NCC produced bythe method of the invention. These include filtration methods usingsurface filters which trap NCC particles. Devices such as a Buchnerfunnel, vacuum filter, rotary vacuum-drum filter, belt filter, or across-flow filter, or screen filters, may be adapted to recover NCC.Centrifugation, dialysis, lyophilization, freeze-drying, or furtherchemical treatments may be performed in some embodiments but are notrequired.

Non-limited embodiments include the following.

A method for making nanocrystalline cellulose (“NCC”) includingcontacting frozen concentrated sulfuric acid with microcrystallinecellulose (“MCC”) at a temperature ranging from about 10° C. to about15° C. for a time sufficient to form a cellulosic paste containinghydrolyzed MCC, diluting the paste containing hydrolyzed MCC in amixture comprising liquid water and water ice to precipitate NCC, andseparating the precipitated NCC from other components in the mixturesuch as water, sulfuric acid, or MCC, thus making NCC.

Flash hydrolysis is fast and hydrolysis may take no more than 1, 2, 3,4, 5, 6, 7, 8, 9, 10 mins after which time it may be terminated byneutralization, acid separation, filtration, dilution, or washing. Insome embodiments, this method will include each of following steps:preparation of MCC before hydrolysis, flash hydrolysis, neutralization,filtration, drying, and grinding.

Unlike prior methods the inventors use concentrated sulfuric acid mostpreferably concentrated to 98.06% wt/wt. Conventional methods avoidusing a high concentration of sulfuric acid to protect cellulosicprecursors from the exothermic effects of exposure to highlyconcentrated acids including highly oxidative conditions and the highexothermic heat release that can quickly carbonize a cellulosicprecursor.

In contrast, the invention ameliorates or avoids the negative effects ofusing a high concentration of sulfuric acid and uses an efficientcooling process to compensate for the heat arising from the hydration ofthe cellulose caused by the acid as well as a short hydrolysis time.

Unlike conventional hydrolysis processes the invention carefullycontrols or compensates for the amount of heat generated by dilution ofthe concentrated sulfuric acid, replacement of hydroxyl groups on MCCand generation of water molecules from hydroxyl ions released from theMCC and the hydrogen ions of the H₂SO₄. Cellulose hydrolysis is attainedwithin a temperature range of −30° C. to 10° C., for example, at −30,−25, −20, −15, −10, −5, 0, 5, 10, 15, 20, 25, or 30° C. or anyintermediate value or subrange within this range; preferably betweenabout 10° C. to 15° C., most preferably about 15° C. The temperature offrozen sulfuric acid or water ice may be selected to attain or maintainthis temperature range. For example, frozen sulfuric acid may have atemperature ranging from <−40, −40, −30, −25, −20, −15, −10, −5, 0 or+3° C. One preferred cooling process includes two parallel routes: usingfrozen H₂SO₄ and using hair-shaped ice.

The quantity, temperature, and shape of the water ice is selected tomaintain a hydrolysis temperature within the desired range, for example,from 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20° C. Ice willgenerally have lower temperature than the desired hydrolysis temperatureto permit removal of excess heat, for example, water ice may have atemperature ranging from <−40, −40, −35, −30, −25, −20, −15, −10, −5, or0° C. which allows it to absorb exothermic and excess heat generated byflash hydrolysis conducted at a higher temperature of 10 to 20° C.

The water ice may be in the shape of granules, scales, or in anelongated form, such as a in a hair shape. In some embodiments ice isused that has an average diameter (granules), thickness (scales) orlength and diameter (elongated) in the range 1, 2, 3, 4, 5, 6, 7, 8, 9,10 mm. Hair-shaped ice may be made by a variety of different methodsincluding that exemplified herein. It may have a ratio of diameter tolength of about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 100, 200,300, 400, 500 or 1,000; and a diameter of 0.01, 0.02, 0.05, 0.1, 0.2,0.1, 0.5, 1.0, 1.2, 1.5 or 2.0 mm as well as any intermediate valuewithin these subranges. In a preferred embodiment, the hair-shaped icewill have a diameter of about 1 mm and a length of about 3 mm.Hair-shaped ice is advantageously used for cooling due to its ability toprovide rapid cooling commensurate with heat release caused by flashhydrolysis. Hair-shaped ice may be made by a variety of differentmethods including that described in the Example below.

Hair-shaped ice may be used for cooling either for the cellulosicprecursor, for sulfuric acid, during hydrolysis, or for a hydrolyzedmixture during or after each process step, including duringneutralization, washing or filtration. Cooling or supercoiling preventsor reduces degradation of the MCC substrate, the NCC product as well asequipment used to process r the substrate MCC into NCC and recover theNCC. For example, cooling prevents discoloration of a paste of MCCsubstrate and sulfuric acid into a brown paste containing oxidized ordegraded cellulose.

In some embodiments of the invention, the MCC precursor is in the formof precooled cellulosic fibers at a temperature of no more than 0, 5,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25° C.The MCC precursor may be dry or prewet.

In other embodiments, the frozen sulfuric acid has a concentration of atleast 50, 60, 70, 80, 90, 91, 92, 93, 94, 95, 96, 97, 98 or >98 mass %.Preferably, the sulfuric acid has a concentration of about 98.06 mass %.Advantageously commercially available concentrated sulfuric acid, suchas sulfuric acid having a concentration of about 98.06 mass % is used.Preferably, sulfuric acid having concentrations of up to 10, 20, 30, 40,50, 60, 70, 80, 90, 95, or <98% are not used.

In some embodiments of the invention, hydrolysis occurs at a temperatureranging from 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19, 20, 21, 22, 23, 24, or 25° C., preferably from about 10° C.to 15° C., more preferably at about 15° C.

In some embodiments, frozen concentrated sulfuric acid and MCC precursoris contacted to form a paste at a wt/wt ratio of frozen concentratedsulfuric acid to MCC of 4:1 to 1:4, 3:1 to 1:3, 2:1 to 1:2, 1.5:1 to1:1.5, or any intermediate ratio value. Preferably, the contactingoccurs at a ratio about 1.25:1 to 1:1.25, more preferably at a ratioabout 1:1.

In some embodiments of the method described above, the diluting occursat a ratio of H₂O to MCC of 4:1 to 1:4, 3:1 to 1:3, 2:1 to 1:2, 1.5:1 to1:1.5 (wt/wt), or any intermediate ratio value; preferably at a ratioranging from 2:1 to 1:2 (wt/wt). Preferably distilled water is used fordiluting, though in some embodiments the water may contain buffers,salts or other solutes, for example a component that facilitates NCCrecovery or neutralization, or other solutes that do not substantiallyinterfere with recovery of NCC.

In other embodiments, separating NCC from a hydrolyzed mixture isperformed by filtering the hydrolyzed MCC to recover NCC; is performedby filtering the hydrolyzed MCC to recover NCC and wherein the filteringis performed at a temperature ranging from 0, 5, 10, 15, 20 to 25° C.(or any intermediate value within this range). In some embodiments thefiltering is performed at a temperature ranging from 0° C. to 15° C.,such as at 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15° C.

In other embodiments, the method described herein further includeswashing the recovered NCC with water or a buffer to increase the pH ofthe NCC. In some embodiments other organic solvents such as ethanol,methanol or aqueous-organic mixtures thereof may be used to wash theNCC. In other embodiments an aqueous solution containing one or moresalts or buffers may be used to wash the NCC; or may further includewashing the recovered NCC with water to increase the pH of the NCC to atleast pH 5.5 to pH 8.5 or any intermediate value within this range suchas pH 5.5, 6.0, 6.5, 6.75, 7.0, 7.25, 7.5, 8.0 or 8.5. In someembodiments, the recovered NCC is washed with water to increase the pHof the NCC to at least pH 6.5 to pH 7.5 and then further dried afterwashing.

In some embodiments, the MCC is contacted directly with the concentratedsulfuric acid to form a paste. In other embodiments, the MCC substratemay be prewet or combined with water that participates in hydrolysis.

In some embodiments, one or more steps of the method may be performedunder conditions than minimize contact of NCC with oxygen, for example,under an inert atmosphere or atmosphere having 0, 1, 2, 5, 10, 15, 16,17, 18, 19, 20 to <21% (or any intermediate value within this range)oxygen or substantially no oxygen at all. Oxidation of NCC may also beinhibited by the addition of an antioxidant.

The method of the invention may produce no more than 10, 20, 30, 40, 50,60, 70, 80, or 90 minutes a yield of NCC of at least about 30, 35, 40,45, 50, 60, 65 wt % based on the weight of the MCC. Advantageously theduration of the contacting, diluting and separating steps in aggregatedo not exceed a batch duration of 15 minutes and yield at least 30, 40,50 or 60 wt % NCC. Here, the batch duration is the time consumed fromthe time when concentrated sulfuric acid is contacted with MCC up to thetime of obtaining a weight unity of cellulose nanocrystals.

Another embodiment of the invention is directed to a compositioncomprising MCC, frozen concentrated sulfuric acid, and water icecrystals, such as hair-ice crystals. Such a composition may have a ratioof MCC precursor to concentration sulfuric acid, or ratio of MCCprecursor to water or water ice as disclosed above.

Other embodiments of the invention include the NCC produced by themethod disclosed herein. The NCC produced may have an average degree ofpolymerization from about 100, 200, 300, 400, 500, 1,000, to about 1,500or any intermediate degree of polymerization within this range and/or besubstantially composed of cellulose I. The NCC may be in a form ofnanocrystalline cellulose or nanofiberous cellulose. In someembodiments, the NCC produced by the method of the invention may be inthe form of “furry” nanocrystal urchins. These may range in furriness(radius/urchin) between 150, 200, 300, 320, 350, 400, 450, 500, 600 ormore and have a mean width ranging from 90, 100, 110, 120, 130, 140,150, 160, 170, 180, 190, 200, 250, or >250 μm. Other physical featuresof NCC produced according to the invention using hair-ice coldhydrolysis may include a crystallinity index (%) ranging from about2.25, 2.3, 2.35, 2.4, 2.42, 2.5, 2.55, 2.6, to 2.65; a crystallite sizeranging from about 2.25, 2.3, 2.35, 2.4, 2.42, 2.45, 2.5, 2.55, 2.6,2.65, to 2.7 nm; and/or a lattice spacing 0.265, 0.270, 0.273, 0.275, or0.28 nm. The NCC produced according to the invention as disclosed hereinpreferably has a negligible amorphous cellulose content, such as lessthan 5, 4, 3, 2, 1, 0.5, or 0.1 wt %.

The NCC produced by the method discloses herein may be used in one ormore of the following ways.

Foods and Pharmaceuticals.

NCC can be used as a tableting or other pharmaceutical excipient. It canalso be used as a low calorie replacement for carbohydrate additivesused as thickeners, flavor carriers and suspension stabilizers in avariety of food products and are useful for producing fillings, crushes,chips, wafers, soups, gravies, puddings and other food products.

Adhesives.

The NCC produced by the method of the invention can be used to enhancethe wet and dry strengths of an adhesive. Through rheology modification,enhanced bond-forming and inherently high strength, NCC can be used toboost performance in wood adhesives such as phenol-formaldehyde andurea/melamine-formaldehyde. NCC may be added to polymeric plastics as afiller or backbone structural material to increase their strength up to10, 20, 50, 100, 200, 500, 1,000, or 2,000 times.

Paper and Non-Wovens.

When used in conjunction with traditional materials in paper production,the NCC produced by the method of the invention can improve productquality. When integrated into super absorbent materials the NCCincreases absorption and improves structural integrity or paper orpaperboard products as well as adsorbent materials. Hygiene productssuch as cosmetic or medical wipes, wound dressings, diapers,incontinence products, sanitary napkins, tampons and other absorbentmaterials may incorporate NCC. NCC may also be used as a barriermaterial in paper and paperboard products, for example, to providegrease or oil-resistance or to enhance retention, dry strength, or wetstrength of the paper or nonwoven product. Nanocrystalline cellulose canbe used to prepare flexible and optically transparent paper. Such paperis an attractive substrate for electronic devices because it isrecyclable, compatible with biological materials and after use anddisposal easily degrades.

The Oil and Gas Industry.

NCC may be incorporated into a variety of oil-field fluids and materialssuch as fracturing fluids, drilling muds and pumping, pressure fluids,as well completion fluids.

Another embodiment of the invention is an apparatus that includes atleast one container suitable for hydrolysis of MCC in the presence offrozen sulfuric acid or sulfuric acid and water, at least one stirrer,and at least one separator; wherein the container comprises a coolingjacket that can be filled with liquid nitrogen, the stirrer is hollowand can be filled with liquid nitrogen, the stirrer is positioned insidethe container, and the separator is operatively connected to thecontainer so that it can receive and separate or recover a precipitateof NCC. These parts may be made of stainless steel or another materialresistant to degradation by sulfuric acid, such as a thermallyconductive polymer.

In some embodiments separate containers will be used to mix concentratedsulfuric acid and MCC and to perform hydrolysis by addition or dilutionwith water. These containers may be operatively attached so that a pasteof MCC and concentrated sulfuric acid can be pumped, sprayed, injected,or otherwise transferred from a first mixing container to a secondhydrolysis container which contains water or water ice or to which wateror water ice is added to flash dilute the paste of sulfuric acid andMCC. The second container for receiving the paste may be equipped with astirrer or other mixing apparatus such as a radial impeller to create aradial flow perpendicular to ingredients to be mixed when introduced asa vertical flow; or a pitch impeller that creates an axial flowperpendicular to ingredients to be mixed when introduced as a horizontalflow into the second container. Preferably stirrers or other mixingapparatuses are refrigerated, for example, by an internal space orcirculation device for internal cooling with liquid nitrogen.

In other embodiments a single container will be used to mix the sulfuricacid and MCC and to contact it or otherwise dilute it with water orwater ice.

The first and/or second containers may be equipped with stirrers or oneor more mixing apparatus such as those described above as well as inletsfor substrate materials, outlets for mixed product, such as outletsoperably attached to a downstream separation or filtration device, orpH, temperature, viscosity or rheological sensors, meters, valves orcontrollers. Temperature controllers may detect and adjust thetemperature of the MCC being hydrolyzed or of NCC-containing productafter hydrolysis. A container or containers used to mix the concentratedsulfuric acid and MCC and for hydrolysis may further be operativelyattached to one or more filters and the filters may be operativeattached to one or more driers. In embodiments with separate mixing andhydrolysis containers, one or both of the containers may be equippedwith a cooling jacket and hollow stirrer as described above andcontrollers may also be employed to adjust the temperature or flow ofliquid nitrogen to a cooling jacket or stirrer so as to maintain adesired hydrolysis temperature in the hydrolysis container.

This apparatus may be further operatively connected to an oven or otherdrier and/or may include at least one separator that is a filter, suchas paper or filter paper.

The apparatus may also comprise a grinder, such as an impact, rotary, orball mill grinder to grind the MCC substrate or dried NCC. In otherembodiments, the MCC or NCC may undergo homogenization ormicrofluidization.

The apparatus may also include a thermostat and/or controller toregulate the mixing ratio of concentrated sulfuric acid to MCC, toregulate the amount of water used to dilute a paste of concentratedsulfuric acid and MCC, or to regulate the mixing time or temperature ofthe concentrated sulfuric acid and MCC or regulate the dilutingtemperature or amount of time between dilution of the paste andseparation of the NCC.

In some embodiments, NCC is produced and recovered without sonication,ultrasonic processing, and/or without centrifugation.

EXAMPLES

The following examples illustrate various aspects of the presentinvention. These examples are not to be construed to limit the claims inany manner whatsoever. As apparent from the examples, the inventionprovides an easy and convenient cooling method to remove excessive heatgenerated by contacting MCC with concentrated sulfuric acid mayotherwise degrade or deform or reduce the yield of the resultingcrystalline NCC product, for instance, by excess heat or oxidation andby converting Cellulose I structure into a Cellulose II structure.Moreover, fine residues of such thermal or oxidative processes can formand cause other technical problems in the subsequent recovery orpurification of NCC, especially during filtration.

As shown below, the invention solves these problems by maintaining theMCC and NCC under conditions with minimize or eliminate decomposition,for example, by providing continuous cooling for the MCC precursor aswell a temperature within a narrow thermal range during hydrolysis, orhydrolysis and filtration, or by use of an inert or reduced oxygenatmosphere.

In a preferred embodiment, cooling using frozen sulfuric acid incombination with fine water ice granules provides a superior MCChydrolysis process because it provides sufficient time for mixing theacid with the MCC precursor before substantial thermal deterioration ofthe MCC precursor by the exothermic heat released by the hydrationeffect of the concentrated H₂SO₄ on the MCC-precursor.

The method of the invention can be performed without requiring complextechniques and devices that are applied for the ordinary schemes ofproduction of NCC which require sonication or centrifugation. The methodof the invention is easily scalable and can be used to produce largequantities of high quality NCC required globally while reducingproduction time and cost.

Example 1 Production of NCC from MCC Using Concentrated Sulfuric Acid

Raw Materials Precursors for microcrystalline cellulose (“MCC”).

Alpha-cellulose isolated from Zyziphus spina var. Christi was used as acellulosic precursor of MCC production. The MCC was conventionallysynthesized using 2N HCl at 80° C. for three hours. This hydrolyzingagent was used to dissolve the amorphous region within the cellulosicmicrofibrils.

Raw Materials Precursors for Nanocrystalline Cellulose.

Microcrystalline cellulose or MCC was used as the precursor for NCCproduction.

The Hydrolysis Process for Synthesizing NCC.

Concentrated sulfuric acid (98.06%), deionized water, fine water icegranules (FWIG) were used for hydrolysis.

Hydrolysis of the MCC to Produce NCC.

Frozen pure concentrated sulfuric acid (98.06%) was mixed with theprecooled MCC at an acid/cellulose ratio of 1:1 (wt/wt) to form a brightwhite paste, see FIG. 1B. The paste was suddenly diluted in a mixture ofcold water and fine water ice granules at a water/cellulose ratio of 1:1(wt/wt) to form a turbid solution which was then filtered under cooling.The filtered NCC precipitate was washed with cold water untilneutralization to pH 7 and then dried to yield NCC.

Characterization of Cellulose Nanocrystals.

The properties of the NCC studied were crystallinity index (CI),crystallite size (CS) and lattice spacing (LS) by XRD, functional groupsby Fourier transform infrared (FTIR), mass loss by thermogravimetricanalysis (TGA) and the energy released and absorbed by differentialthermal analysis (DTA).

Sample Preparation for the Different Properties Determinations.

The NCC samples specified for XRD, FTIR and TGA were ground in a ballmill to passes through a 100 mesh and retained on a 120 mesh. For theNCC samples chosen for SEM and TEM spectroscopies, NCC solutions weredispersed into absolute ethanol at a concentration of 1% wt/wt andsonicated for an hour. A clear droplet was mounted onto an Al-stub forSEM or onto a copper grid for TEM tests.

The Optical Vision System.

The optical speculation unit used to study the NCC samples consists of alight microscope (CE-MC200A) with a magnification power of 10× withsuitable vision system (OPTIKA PRO 5 Digital Camera-4083.12). Vision PRO4 software was used to pick up and process images.

Scanning Electron Microscopy (SEM).

SEM spectroscopy was used to investigate the surficial morphology aswell as anatomical features of the NCC. The samples were placed ontodouble side-carbon tape on Al-stub and air-dried. All samples weresputtered, before examination, with about 15 nm thick gold layer (JEOLJFC-1600 Auto Fine Coater) in a vacuum chamber (Tang et al., 1997). TheNCC samples were tested using a SEM Quanta FEG 450, FEI, Amsterdam,Netherlands. The microscope was operated at an accelerating voltagewhich varied from 5-20 kV.

Transmission Electron Microscopy (TEM).

TEM spectroscopy of the NCC samples was done to visualize theircomponent building blocks leading to the final architecture formed viatheir crystal growth. Phosphotungstic acid was used to dye the NCCsamples. The NCC was examined by TEM (JEM-1011 JEOL, Japan) at anoperated voltage of 100 kV.

The X-Ray Diffraction (XRD).

The XRD spectra of the NCCs were studied to determine theircrystallinity using the XRD-D2 Phaser Bruker (USA). The generator wasoperated at 30 KV and 30 mA for a period of 50 minutes using CuKaradiation with a wavelength of 0.15418 nm. The tests were done in thereflection mode at a scan speed of 4°/min in steps of 0.05°. All sampleswere scanned between 2θ=4° to 30°, see Hindi, 2017a, id.

The Crystallinity Index (CI).

First, individual crystalline peaks were isolated using thecurve-fitting process from the diffraction intensity profiles asdescribed by Park et al., 2010, id.; Garvey, C. J., Parker, I. H., andSimon, G. P. 2005. On the interpretation of X-ray diffraction powderpatterns in terms of the nanostructure of cellulose I fibres,Macromolecular Chemistry and Physics. 206 (15): 1568-1575, 2005. DOI:10.1002/macp.200500008; and Hult, E. L., Iversen, T., and Sugiyama, J.2003. Characterization of the supenmolecular structure of cellulose inwood pulp fibers. Cellulose. 10 (2): 103-110, 2003, each incorporatedherein by reference in their entirety.

The CI was calculated by dividing the diffractogram area of crystallinepeaks on the total area of the whole diffractogram. The area under thewhole curve was estimated by summing of adjacent trapezoids using Excel(Microsoft, USA) as indicated by Hindi (2017^(a)), id.

The Crystallite Size (CS).

The CS (nm) of the NCC backbone was calculated by Scherrer equation withrespect to the crystallographic plane, namely 002 as follow:CS=Kλ/β_(1/2) Cos θ, where K is the correction factor and normally isconsidered to be 0.91, λ is the radiation wavelength, θ is thediffraction angle, and β_(1/2) is the corrected angular full width athalf maximum (FWHM) in radiansHindi, 2017^(a), id.

Lattice Spacing (LS).

Bragg's equation was used to calculate LS value as shown below: LS=n λ/2sin θ, where n is an ordinal number expressed by the value of “1” fordiffractograms having the strongest intensity, λ is the wavelength ofX-rays hit with the crystal (0.1542 nm), and θ is the Bragg's anglerelated to the 200-plane, Hindi, 2017^(a), id.

Fourier Transform Infrared (FTIR) Spectroscopy.

The FTIR was used to study the chemical groups of the NCC using a BrukerTensor 37 FTIR spectrophotometer. The MCC samples were oven-dried at100° C. for 4-5 h, mixed with KBr in a ratio of 1:200 (w/w) andcompressed under vacuum into pellets. The FTIR-spectra were recorded inthe transmittance mode in the range of 4000-500 cm⁻¹.

Thermal Analysis.

Thermogravimetric analyses (TGA) of the NCC were applied by using aLinseis STA PT1000 analyzer. Heating scans were considered from 30 up to550° C. at 20° C./min in a flowing nitrogen atmosphere for the NCC;Hindi, 2017^(b,c), id.

Statistical Design and Analysis.

Completely randomized design with three replications was performed inthe present investigation using the analysis of variance procedure andleast significant difference test (LSD) at P≤0.05 according to Steel andTorrie (1980). See Steel, R. G. D. and Torrie, T. H. 1980. Principlesand procedures of statistics, N.Y., USA, incorporated herein byreference in its entirety.

Characterization of the NCC

Microscopic Characterization.

The NCC produced according to the invention as disclosed was found toextend its crystal growth in an acidic media when a droplet was mountedon a glass substrate up to an urchin-shaped architecture; see FIGS.2A-2D. For the urchin-shaped NCCs as described by Table 2 and FIG. 1,the centric urchins produced by hot hydrolysis had the highest width of426.21 μm and the lowest furriness of 70 radius/urchin. On the otherhand, the dwarf centric urchins had the lowest width of 70.12 μm and thehighest furriness of 700 radius/urchin. In between, the NCCs obtained byhair ice-cold hydrolysis had medium values of width and furrinessbetween the other hydrolysis schemes of 134.2 μm and 320 radius/urchin,respectively. Cryogenic hydrolysis was found to enhance the crystalgrowth by increasing hydrogen bonds within the CNCs lattice thatfacilitate their agglomeration into microcrystalline form and subsequentease collection by ordinary filtration without needing to centrifugationor sonication. This procedure was performed in a sudden coolingconditions that permitted precipitation of the NCC-crystals in areasonable yield (38.8%) from the microcrystalline cellulose synthesizedfrom leaflets of date palm fronds (Phoenix dactylifera L.) discardingboth sonication and centrifugation processes.

SEM micrographs of these structures are shown by FIGS. 3A-3D and atransmission electron micrograph (TEM) is depicted by FIG. 4.

X-Ray Diffraction (XRD).

It is clear from FIG. 5 that X-rayed NCC exhibited a principle sharppeak around 2θ=21.13° representing the 200 reflection related to thecrystalline materials such as hemicelluloses and alpha-cellulose. Inaddition, the NCC sample showed two broad peaks at 2θ=18.29° and 19.26°representing 110 and 11 0 reflections. Accordingly, the similaritybetween the resultant NCCs and cellulose-I was clear, especially withrespect to the crystallographic planes, namely 110, 11 0 and 200 asindicated in FIG. 5; see Wada, M., Heux, L., and Sugiyama, J. 2004.Polymorphism of cellulose I family: Reinvestigation of cellulose IV.Biomacromolecules, 5: 1385-1391; Chen, W. S., Yu, H. P., Liu, Y. X.,Chen, P., Zhang, M. X., and Hai, Y. F. 2011. Individualization ofcellulose nanofibres from wood using high-intensity ultrasonicationcombined with chemical pretreatments. Carbohydr. Polym., 83: 1804-1811;Kumar et al. 2014, id., and Hindi, 2017^(a,b), id, each incorporatedherein by reference in their entirety.

Crystallinity Index (CI).

The CI or crystallinity index of the NCC was found to be high at 86%.This value approaches to that for the MCC precursor. Both materialsretained only the crystalline regions of the parent cellulosicmicrofibrils after removal of the amorphous regions by the method of theinvention. The obtained CI was higher than the cellulose and NCC (70.62and 76.01%, respectively) estimated by Wulandari et al. (2016) or woodpine (70%) determined by Borysiak and Doczekalska (2005), and lieswithin the CI ranges (41.5% to 95.5%) calculated by Park et al. (2010),id., and approaches to that calculated by Chen et al. (2017), id. SeeWulandari, W. T., Rochliadi, A., and Arcana, I. M. 2016. Nanocelluloseprepared by acid hydrolysis of isolated cellulose from sugarcanebagasse. IOP Conf. Series. Materials Science and Engineering, 107:012045 doi:10.1088/1757-899X/107/1/012045; Borysiak, S. and Doczekalska,B. 2005. X-ray diffraction study of pine wood treated with NaOH. Fibersand Textiles in Eastern Europe, 5 (53): 87-89; Park, S., Baker, J. O.,El-Himmell, M., Parilla, P. A., and Johnson, D. K. 2010. Cellulosecrystallinity index: Measurement techniques and their impact oninterpreting cellulase performance. Biotechnology for Biofuels. 3. 10.DOI: 10.1186/1754-6834-3-10; and Chen, Y. W., Tan, T. H., Lee, H. V.,and Abd Hamid, S. B. 2017. Easy fabrication of highly thermal-stablecellulose nanocrystals using Cr(NO ₃)³ catalytic hydrolysis system: Afeasibility study from macro-to nano-dimensions. Materials, 10: 42.DOI:10.3390/ma10010042, each incorporated herein by reference in theirentirety.

Crystallite Size (CS).

The CS is the crystallite thickness estimated by the Scherrer formulafor small crystallites with less than 100 nm width. The average CS ofthe NCC was determined to be 2.8 nm which is similar to that found byHindi, but smaller than that for cellulose I (about 5 nm in width). Thisfinding agrees with the range estimated by Hindi (2017^(a,c), id).

Lattice Spacing (LS).

The LS of the NCC is a distance between their successive strata within acrystallite using the Bragg's equation. See Clair, B., Almeras, T.,Yamamoto, H., and Okuyama, J. 2006. Mechanical behavior of cellulosemicrofibrils in tension wood, in relation with maturation stressgeneration. Biophysics Journal, 91 (3): 1128-1137. DOI:10.1529/biophysj.105.078485, incorporated herein by reference in itsentirety. The LS was estimated to be 0.214 nm. Since larger crystal sizeleads to a larger LS between its strata, the lower LS value can beattributed to the small size of the NCC crystallite estimated in thepresent invention (2.8 nm). See Davidson, T., Newman, R. H., and Ryan,M. J. 2004. Variations in the fibre repeat between samples of celluloseI from different sources. Carbohydrate Research, 339 (18), 2889-2893.DOI: 10.1016/j.carres.2004.10.005, incorporated herein by reference inits entirety. The LS value was slightly smaller than that found by Hindi(2017^(a,c), id).

Fourier Transform Infra-Red (FTIR) Spectroscopy.

The FTIR characterization is an indicator for any changes in chemicalfunctionality of the MCC precursor via its H₂SO₄-hydrolysis to produceNCC; see FIG. 6. The FTIR spectra showed distinct absorption bands ofchemical groups of the NCC. All samples presented two main absorbanceregions between about 800-1800 cm⁻¹ to 2800-3500 cm⁻¹. The FTIR spectraof all samples showed sharp bands around the following wavenumbers:

at 1109 cm⁻¹ due to C—C ring stretching band (˜1155 cm⁻¹) and C—O—Cglycosidic ether band (1105 cm⁻¹) (Kumar et al., 2014; Mandal, Arup, andDebabrata Chakrabarty. Isolation of nanocellulose from waste sugarcanebagasse (SCB) and its characterization. Carbohydrate Polymers 86, no. 3(2011):1291-1299; Garside, P. and Wyeth, P., 2003. Identification ofcellulosic fibres by FTIR spectroscopy-thread and single fibre analysisby attenuated total reflectance. Studies in Conservation, 48(4), pp.269-275; Nelson, M. L. and O'Connor, R. T., 1964a. Relation of certaininfrared bands to cellulose crystallinity and crystal latticed type.Part I. Spectra lattice types I, II, III and of amorphous cellulose.Journal of Applied Polymer Science, 8(3), pp. 1311-1324.

at 1468 cm⁻¹ due to scissoring motion of the CH₂-group in the NCC (Kumaret al., 2014; Mandal and Chakrabarty. 2011; Garside and Wyeth. 2003;Nelson and O'Connor, 1964^(a;); Nelson, M. L. and O'Connor, R. T., 1964.Relation of certain infrared bands to cellulose crystallinity andcrystal lattice type. Part II. A new infrared ratio for estimation ofcrystallinity in celluloses I and II. Journal of Applied PolymerScience, 8(3), pp. 1325-1341;

at 1636 cm⁻¹ due to O—H bending of the absorbed water (Kumar et al.,2014; Khalil et al., 2001; Moran et al., 2008; Troedec et al., 2008;Zain et al., 2014; Costa et al., 2015);

at 1737 cm⁻¹ due to C—O stretching vibration for the acetyl and esterlinkages (Kumar et al., 2014);

at 2853-2922 cm⁻¹ due to C—H stretching (Kumar et al., 2014; Khalil etal., 2001; Zain et al., 2014); and

at 3439 cm⁻¹ due to O—H stretching (axial vibration) intramolecularhydrogen bonds for cellulose I. See Costa, L. A. de S., Fonseca, A. F.,Pereira, F. V. and Druzian, J. I. 2015. Extraction and characterizationof cellulose nanocrystals from corn stover. Cellulose Chem. Technol. 49(2): 127-133; Dong, X. M., Revol, J. F., Gray, D. 1998. Effect ofmicrocrystallite preparation conditions on the formation of colloidcrystals of cellulose. Cellulose. 5: 19-32; and Khalil, H., Ismail, H.,Rozman, H. and Ahmad, M. 2001. The effect of acetylation on interfacialshear strength between plant fibres and various matrices. Eur. Polym 37,1037-1045; Li, J. et al. 2014. Homogeneous isolation of nanocellulose bycontrolling the shearing force and pressure in microenvironment.Carbohyd. Polym. 113: 388-399; Moran, J. I., Alvarez, V. A., Cyras, V.P., and Vazquez, A., 2008. Extraction of cellulose and preparation ofnanocellulose from sisal fibers, Cellulose. 15: 149-159; Troedec, M.,Sedan, D., Peyratout, C., Bonnet, J., Smith, A., Guinebretiere, R.,Gloaguen, V., and Krausz, P. 2008. Influence of various chemicaltreatments on the composition and structure of hemp fibers, CompositesPart A-Appl. Sci. Manufact. 39: 514-522; and Zain, N. F. M., Yusop, S.M. and Ishak Ahmad, I. 2014. Preparation and characterization ofcellulose and nanocellulose from pomelo (Citrus grandis) albedo. NutrFood Sci. 5:1. doi:10.4172/2155-9600.1000334, each incorporated hereinby reference in their entirety.

Based on the spectral results, the inventors confirmed that NCC has anegligible amorphous cellulose content and is composed of crystallinecellulose I, similar to the MCC precursor cellulose.

Thermogravimetric Analysis (TGA).

The TGA thermogram of the NCC in FIG. 7 showed a gradual increase intheir mass loss upon rising temperature from 25° C. up to 500° C. inflowing N₂-gas. This range was divided into five separated regions,namely 25-100° C., 100° C.-200° C., 200° C.-300° C., 300° C.-400° C.,and 400° C.-500° C. to study the NCC-mass loss occurred at each regimedue to the thermal effect. The NCC lost about 5% of its origin weightbetween 25° C. to 100° C. due to evaporation of free water (Hindi,2017^(b), id.). Furthermore, mass of the NCC was lost by about 22% oftheir parent mass when the temperature was raised from 100° C. to 200°C. due to evaporation of both hygroscopic and constitutional water. Inaddition, between 200° C.-300° C., the NCC mass loss was about 12%. Withincreasing temperature, the NCC continued to lose additional mass as 25%and 17% for the 4th (300° C.-400° C.) and 5th (400° C.-500° C.) regions,respectively. Furthermore, the sulfate groups in sulfated-NCC requiredless energy to be eliminated (Julien et al., 1993), therefore,H₂SO₄-molecules are formed at lower temperatures than those at highertemperatures. See Julien, S., Chomet, E., and Overend, R. P. 1993.Influence of acid pre-treatment (H ₂ SO ₄ , HCl, HNO ₃) on reactionselectivity in the vacuum pyrolysis of cellulose. Journal of Analyticaland Applied Pyrolysis, 27(1), 25-43, incorporated herein by reference inits entirety.

Differential Thermal Analysis (DTA).

DTA is a measuring tool to differentiate two hot materials. Here, thefirst one is the NCC and the second one is an inert reference material.Both materials are found at the same place and conditions. As shown inFIG. 8, there was an endothermic peak found under the baseline and oneexothermic peak present above this line. The endothermic peak beginsfrom 40° C. up to 270° C. with a maximum shift at 150° C., while theexothermic peak starts from 270° C. until 450° C. with a maximum valueat 340° C.; see FIG. 8 and Table 1.

The endotherm of the DTA thermogram can be attributed to evaporation ofthe three forms of moisture content in the NCCs—free, hygroscopic andconstitutional moisture—besides fusion or melting process of the NCC.For the sulfated NCC, the hydrolyzing agent used was H₂SO₄ that acted asa dehydrating agent helping for grafting the hydrophobic sulfate groupsthat lowering their moisture affinity. Accordingly, after the acidhydrolysis of the MCC, only nanoscale cellulose crystals would possessthe sulfate groups responsible for the higher onset temperature ofcrystal melting with wider endotherm.

The exotherm can be attributed to the depolymerization of the sulfatedNCC, decomposition of glycosyl units and then formation of carbonaceousparticles (Kumar et al., 2014). This depolymerization can be attributedto four effects: (a) the nanosize and the huge number of the free endsof the NCC-chains which were decomposed at lower temperatures, (b) H₂SO₄that is a dehydrating agent that facilitates the depolymerization of NCCby elimination of some hydroxyl groups, (c) the presence of H⁺ protonsin the weak acidic atmosphere which may be responsible on increasing thecarbonaceous residues, and (d) the highly crystalline nature of the NCCincreased in the carbonaceous residues. See Wada et al., 2004, andGeorge, J., Ramana, K. V., Bawa, A. S., and Siddaramaiah. 2011.Bacterial cellulose nanocrystals exhibiting high thermal stability andtheir polymer nanocomposites. Internl. J. Biologic. Macromol., 48:50-57, each incorporated herein by reference in their entirety.

As mentioned above, the NCC produced by the method of the invention wasfound to extend its crystal growth, in an acidic media when a dropletwas mounted on a glass substrate, up to a urchin-shaped architecture.The X-rayed NCC exhibited a principle sharp peak around 2θ=21.13°representing the 200 reflection related to the crystalline materials(hemicelluloses and alpha-cellulose) as well as two broad peaks at2θ=18.29° and 19.26° representing 110 and 11 0 reflections. This showsthe high similarity between the resultant NCC and cellulose-I,especially when regarding the crystallographic planes, namely 110, 11 0and 200. For the thermogravimetric thermogram of the NCC, there is anendothermic peak found under the baseline, while one exothermic peak ispresent above this line. The thermogravimetric thermogram of the NCCshowed a gradual increase in their mass loss upon rising temperaturefrom 25° C. up to 500° C. in a flowing N₂ gas.

In addition, the absolute value of the heat change for the endothermswas estimated to be 639 μVs/mg that is extremely higher than that theexotherm (37 μVs/mg). Since the material absorbing higher energy aremore thermally stable than those absorbing lower energy or releasingmore energy (Hindi, et al, 2017), the NCC have excellent thermalstability.

TABLE 1 Differential thermal analysis (DTA) for temperature range (TR),maximum temperature (MT) and enthalpy change (EC) of the nanocrystallinecellulose (NCC) upon thermal degradation up to 500° C. Thermogram MT EGNo type TR (° C.) (° C.) (μVs/mg) 1 Endotherm  40-270 150 −640 2Exotherm 270-450 340 38

TABLE 2 Comparison of conventional NCC production with the ExampleCellulose Nanocrystal (CNC) production Source of Conventional variationMethods Example (invention) Using sulfuric acid Used Used Sulfuric acid60-64% 98.06% concentration (wt/wt) Acid/cellulose ratio 8:1 1:1Hydrolysis temperature 50-100° C. Cooling to 10° to 15° C. with finewater ice granules Sonication Used Not Used Centrifugation Used Not UsedImmediately after production of nanosized crystals Crystals isolationcentrifugation filtration Batch duration* 4 hours 10 minutes NCC yield8-20 wt % 60 wt % based on weight of the MCC precursor *The timeconsumed from adding acid up to obtaining the weight unity of cellulosenanocrystals.

As apparent from the comparison above in Table 2, the method of theinvention provides a fast and simple production scheme for NCC which canbe performed without complex requiring instruments such as centrifugesor sonicators. The use of simple separation steps to recover NCC, suchas use of filter paper or sinter glass filters and Gooch filtration,eliminates the need for these devices simplifies production and reducesequipment and maintenance costs. The method of the invention alsoreduces the amount of sulfuric acid needed by conventional processesfurther reducing costs. Moreover, it is unnecessary to prewet acellulosic substrate prior to contacting it with concentrating sulfuricacid.

Use of a flash-hydrolysis method according to the invention provideshydrolysis within a narrow temperature range, such as between 10° C. and15° C. and is quenched with the addition of inexpensive and non-toxicwater and water ice. Degradation of MCC once treated with theconcentrated sulfuric acid was minimized or eliminated in the presenceof frozen sulfuric acid. Moreover, the inventors found that crystal sizeof the NCC could be controlled by simply adjusting the temperature ofeither the hydrolysis or subsequent separation (e.g., filtration) of theNCC.

The method of the invention provides for a highly pure NCC substantiallyfree of amorphous cellulosic regions and an NCC product that retainsCellulose I structure despite treatment with concentrated sulfuric acid.Moreover, the method of the invention provides for grafting or up tothree sulfate groups onto the available carbon sites (no's 3, 4, and 6)of the glucopyranose unit constituting the cellulose chain. A highcontent of grafted sulfate groups can generate high electrostaticcharges in the resulting NCC product.

The properties and advantages described herein provide a method that canbe industrially scaled to produce large quantities of NCC at a low cost.

Example 2 Characterization of NCC Synthesized Using Three DifferentHydrolysis Schemes

NCC was produced by the method of the invention and by conventional hothydrolysis and cryogenic cold hydrolysis. The NCC product of the presentinvention prepared using hair ice-cold hydrolysis was characterized byoptical microscopy, X-Ray Diffraction (XRD) as well as Fourier TransformInfrared (FTIR) Spectroscopy and then compared to NCC productsynthesized by the traditional method of hot hydrolysis and cryogeniccold hydrolysis.

The Optical Vision System.

The optical speculation unit used consisted of a light microscope(CE-MC200A) in a magnification power of 10× with suitable vision system(OPTIKA PRO 5 Digital Camera-4083.12) using a Vision PRO 4 software topick up and process images as well as to record different measurementsof the cellular dimensions in a micrometer scale. In addition, thesoftware was also used to show the light intensity of the images.

It was found that different nanocrystalline cellulose (NCCs)constructions, which were termed as urchins, were formed upon crystalgrowth in an acidic media on a glass slide. The difference between theurchins depended on the cooling procedure used through the hydrolysisscheme applied.

TABLE 3 Mean values¹ for width and furriness of the urchins produced bythe three hydrolysis schemes upon a droplet shrinking on a glass slidein an acidic media. Hydrolysis scheme Width (μm) Furriness(radius/urchin) Hot hydrolysis² 426.21^(A)  70^(C) Hair ice-coldhydrolysis³ 134.2^(B) 320^(B) Cryogenic-cold hydrolysis⁴ 70.12^(C)700^(A) ¹Means with the different letter at the same column are differedsignificantly at 5% Level. ²Hindi, 2017^(d). ³The present invention.⁴Hindi and Abohassan, United States Patent Application 20170291962.

FIGS. 2B-2D show different urchin shaped constructions synthesized bythe three hydrolysis schemes. In FIG. 2B large urchins were synthesizedby hot hydrolysis and in FIGS. 2C and 2D dwarf urchins synthesized bycryogenic acid hydrolysis.

As described above, for the urchin-shaped NCCs described in Table 3 andFIGS. 2B-2D, the centric urchins produced by hot hydrolysis had thegreatest width of 426.21 μm and the lowest furriness of 70radius/urchin. On the other hand, the dwarf centric urchins had thelowest width of 70.12 μm and the highest furriness of 700 radius/urchin.In between, the NCCs obtained by hair ice-cold hydrolysis had mediumvalues of width and furriness between the other hydrolysis schemes,namely 134.2 μm and 320 radius/urchin, respectively.

The inventors found that cryogenic hydrolysis enhanced the crystalgrowth by increasing hydrogen bonds within the CNCs lattice thatfacilitated agglomeration into a microcrystalline form and subsequentlyfacilitated collection by ordinary filtration without centrifugation orsonication. This procedure was performed under sudden cooling conditionsthat permitted precipitation of the NCC crystals in a reasonable yieldof 38.8% from the microcrystalline cellulose synthesized from leafletsof date palm fronds (Phoenix dactylifera L.) without sonication orcentrifugation.

XRD.

The XRD spectra of the fibers were used to study sample crystallinityusing the XRD-D2 Phaser Bruker (USA). The generator was operated at 30KV and 30 mA. The samples were exposed for a period of 3000s using CuKaradiation with a wavelength of 0.15418 nm. The sample crystallinity isdefined as the ratio of the amount of crystalline cellulose to the totalamount of sample material including crystalline and amorphous segments.All the experiments were performed in the reflection mode at a scanspeed of 4°/min in steps of 0.05°. All samples were scanned in a 2θ=26°range varying from 4° to 30°; see Hindi, S. S. Z. 2017^(a),Microcrystalline cellulose: The inexhaustible treasure forpharmaceutical industry. Nanoscience and Nanotechnology Research. 4 (1):22-31. 10.12691/nnr-4-1-3; Hindi, S. S. Z. 2017^(b) . Differentiationand Synonyms Standardization of Amorphous and Crystalline CellulosicProducts. Nanoscience and Nanotechnology Research. 2017; 4(3):73-85.doi: 10.12691/nnr-4-3-1.

The XRD pattern showed a principle sharp peak around two theta of about22.6° for the three hydrolysis schemes which are supposed to representthe typical cellulose-I structure. The nanocellulosic crystals exhibitedcharacteristic assignments of 110, 200, and 004 planes, respectively;Wada, M., Heux, L., and Sugiyama, J. 2004. Polymorphism of cellulose Ifamily: Reinvestigation of cellulose IV. Biomacromolecules. 5:1385-1391; Chen, W. S., Yu, H. P., Liu, Y. X., Chen, P., Zhang, M. X.,and Hai, Y. F. 2011. Individualization of cellulose nanofibres from woodusing high-intensity ultrasonication combined with chemicalpretreatments. Carbohydr. Polym. 83: 1804-1811; Kumar, S., Saha, T.,Sharma, S. 2015. Treatment of pulp and paper mill effluents using novelbiodegradable polymeric flocculants based on anionic polysaccharides: anew way to treat the waste water. Int Res J Eng Technol. 2 (4):1-14).The XRD analyses revealed that the NCCs had the same crystallinestructure of cellulose-I.

Crystallinity Index.

Individual crystalline peaks were first extracted by a curve-fittingprocess from the diffraction intensity profiles. The CI was calculatedby dividing the diffractogram area of crystalline cellulose by the totalarea of the original diffractogram. The area under the curve wasestimated by summing of adjacent trapezoids using Excel (Microsoft, USA)as described by Hindi, S. S. Z. 2017^(c) ; Some Promising Hardwoods forCellulose Production: I. Chemical and Anatomical Features. Nanoscienceand Nanotechnology Research. 2017; 4(3):86-97. doi:10.12691/nnr-4-3-2.). The crystallinity index of the NCCs synthesized byhot hydrolysis (85.9%) was higher than those synthesized by hairice-cold hydrolysis (82.6%), and cryogenic hydrolysis (80.2%).

Crystallite Size (CS).

The CS is the NCCs crystallite thickness (nm) determined by the Scherrerequation when the crystals are smaller than 100 nm; Ciupina, V.,Zamfirescu, S., and Prodan, G. 2007. Evaluation of mean diameter valuesusing Scherrer equation applied to electron diffraction images, In:Nanotechnology-Toxicological Issues and Environmental Safety, NATOScience for Peace and Security Series, 231-237. DOI:10.1007/978-1-4020-6076-2_15. The CS was calculated with respect to thecrystallographic plane, namely 002 as follows: CS=Kλ/β_(1/2) Cos θ,where K is the correction factor and usually taken to be 0.91, λ is theradiation wavelength, θ is the diffraction angle, and β_(1/2) is thecorrected angular full width at half maximum (FWHM) in radians; Hindi,S. S. Z. 2017^(c) , Some Promising Hardwoods for Cellulose Production:I. Chemical and Anatomical Features. Nanoscience and NanotechnologyResearch. 2017; 4(3):86-97. doi: 10.12691/nnr-4-3-2). The averagecrystallite size of the NCCs didn't significantly differ due to thecellulosic product although there was a descending trend from the hot upto the cryogenic hydrolysis (Table 3).

Lattice Spacing (LS).

The averages LS of the NCCs didn't differ significantly due to thecellulosic product although there is a descending trend from the hot upto the cryogenic hydrolysis (Table 3).

TABLE 4 Main values of the important crystallographic properties of theNCCs synthesized by the three hydrolysis schemes. CrystallinityCrystallite size Lattice Hydrolysis scheme Index, % nm spacing nm Hothydrolyzed² 85.9 2.99 0.202 (1.094)¹ (0.142) (0.014) Hair ice-coldhydrolyzed³ 82.6 2.42 0.273 (0.984) (0.098) (0.057) Cryogenic-coldhydrolyzed⁴ 80.2 2.15 0.298 (1.297) (0.131) (0.063) ¹Standard deviation²Hindi, 2017^(d). ³the present invention. ⁴Hindi and Abohassan patent.

FTIR Spectroscopy.

The FTIR was used to investigate chemical structure of the NCCs samplesusing a Bruker Tensor 37 FTIR spectrophotometer. The samples wereoven-dried at 100° C. for 4-5 h, mixed with KBr in a ratio of 1:200(w/w) and pressed under vacuum to form pellets. The FTIR-spectra of thesamples were recorded in the transmittance mode in the range of 4000-500cm⁻¹.

As reviewed by Hindi, S. S. Z. 2017^(d) . Suitability of date palmleaflets for sulphated cellulose nanocrystals synthesis. Nanoscience andNanotechnology Research, 2017, Vol. 4, No. 1, 7-16.DOI:10.12691/nnr-4-1-2, changes in chemical functionality afterH₂SO₄-hydrolysis of the leaflets of date palm were obtained by FTIRspectroscopy. The spectra of the resultant NCCs synthesized by the threehydrolysis schemes showed absorption bands of chemical groupscharacteristic of the crystalline product. All samples presented twomain absorbance regions in the range of about 800-1800 cm⁻¹ to 2800-3500cm⁻¹. The FTIR spectra of all samples have shown sharp bands around thefollowing wavenumbers:

-   -   1108.46 cm⁻¹ due to C—C ring stretching band (˜1155 cm⁻¹) and        C—O—C glycosidic ether band (1105 cm⁻¹).    -   1467.21 cm⁻¹ due to scissoring motion of the CH₂-group in the        SCNCs.    -   1635.13 cm⁻¹ due to O—H bending of the absorbed water.    -   1737.31 cm⁻¹ due to C—O stretching vibration for the acetyl and        ester linkages.    -   2852.45-2921.49 cm⁻¹ due to C—H stretching.    -   3438.08 cm⁻¹ due to O—H stretching (axial vibration)        intramolecular hydrogen bonds for cellulose I.

Based on the spectral data, it can be confirmed that the NCCssynthesized by the three hydrolysis schemes are composed of crystallinecellulose I while content of amorphous cellulose is negligible.

Example 3

Production of Hair-Shaped Ice.

Massive Ice Preparation.

Using a deep freezer maintained at −32° C. for 6 hours, distilled waterin a suitable stainless steel containers (660 ml) was frozen.

Ice Lumps Preparation.

A crusher was used to fracture the massive ice into smaller pieces orice lumps having a mean diameter of about 4 cm.

Hair-Shaped Ice Isolation.

Using a precooled-high speed mixer with very thin and sharp knives, theice lumps were cut into smaller particles about 1 mm in diameter. Theabout 1 mm-ice particles were sieved to exclude excess free water andprovide a homogeneous ice particle size. The 1 mm ice particles weremildly compressed in a manual compressor in a stainless steel capsulefor 1 minute at a compression pressure of 30 psi under cooling at 0° C.in an isolated atmosphere to form icy scales (3 mm longitudinally, 1 mmradially, and 1 mm tangentially). The pressure was maintained using ascrew system and the capsule was cooled for 15 min at −32° C.

Splitting the Icy Scales into Icy Hairs.

The automated compressor using interlocked knives—movable knivesalternated with stationary ones—and fixed between the two boards of thecompressor was used to form the hair shape ice to about 3 mm in length,and 1 mm in width. The compression process excludes free water with anaim of cold vacuum filtration. The dehydrated hair-shaped ice refers toice granules free of any free water surrounding their particles. Thiselimination of the free water can be done by vacuum-cold filtration. Thevacuum aid is necessary to exclude the existent free water rapidly,while the cooling aid is essential to prevent melting ice to produceexcess of free water. In addition, the cooling process freezes thehygroscopic water films enveloping the ice particles. This is due tothat heat enthalpy of the free and hygroscopic water is higher than thatof the ice itself. Accordingly, the obtained hair ice has the maximumcooling ability comparing to other forms of water ice.

Terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention.

The headings (such as “Background” and “Summary”) and sub-headings usedherein are intended only for general organization of topics within thepresent invention, and are not intended to limit the disclosure of thepresent invention or any aspect thereof. In particular, subject matterdisclosed in the “Background” may include novel technology and may notconstitute a recitation of prior art. Subject matter disclosed in the“Summary” is not an exhaustive or complete disclosure of the entirescope of the technology or any embodiments thereof. Classification ordiscussion of a material within a section of this specification ashaving a particular utility is made for convenience, and no inferenceshould be drawn that the material must necessarily or solely function inaccordance with its classification herein when it is used in any givencomposition.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

It will be further understood that the terms “comprises” and/or“comprising,” when used in this specification, specify the presence ofstated features, steps, operations, elements, and/or components, but donot preclude the presence or addition of one or more other features,steps, operations, elements, components, and/or groups thereof.

As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items and may be abbreviated as“/”.

Links are disabled by deletion of http: or by insertion of a space orunderlined space before www. In some instances, the text available viathe link on the “last accessed” date may be incorporated by reference.

As used herein in the specification and claims, including as used in theexamples and unless otherwise expressly specified, all numbers may beread as if prefaced by the word “substantially”, “about” or“approximately,” even if the term does not expressly appear. The phrase“about” or “approximately” may be used when describing magnitude and/orposition to indicate that the value and/or position described is withina reasonable expected range of values and/or positions. For example, anumeric value may have a value that is +/−0.1% of the stated value (orrange of values), +/−1% of the stated value (or range of values), +/−2%of the stated value (or range of values), +/−5% of the stated value (orrange of values), +/−10% of the stated value (or range of values),+/−15% of the stated value (or range of values), +/−20% of the statedvalue (or range of values), etc. Any numerical range recited herein isintended to include all subranges subsumed therein.

Disclosure of values and ranges of values for specific parameters (suchas temperatures, molecular weights, weight percentages, etc.) are notexclusive of other values and ranges of values useful herein. It isenvisioned that two or more specific exemplified values for a givenparameter may define endpoints for a range of values that may be claimedfor the parameter. For example, if Parameter X is exemplified herein tohave value A and also exemplified to have value Z, it is envisioned thatparameter X may have a range of values from about A to about Z.Similarly, it is envisioned that disclosure of two or more ranges ofvalues for a parameter (whether such ranges are nested, overlapping ordistinct) subsume all possible combination of ranges for the value thatmight be claimed using endpoints of the disclosed ranges. For example,if parameter X is exemplified herein to have values in the range of 1-10it also describes subranges for Parameter X including 1-9, 1-8, 1-7,2-9, 2-8, 2-7, 3-9, 3-8, 3-7, 2-8, 3-7, 4-6, or 7-10, 8-10 or 9-10 asmere examples. A range encompasses its endpoints as well as valuesinside of an endpoint, for example, the range 0-5 includes 0, >0, 1, 2,3, 4, <5 and 5.

As used herein, the words “preferred” and “preferably” refer toembodiments of the technology that afford certain benefits, undercertain circumstances. However, other embodiments may also be preferred,under the same or other circumstances. Furthermore, the recitation ofone or more preferred embodiments does not imply that other embodimentsare not useful, and is not intended to exclude other embodiments fromthe scope of the technology. As referred to herein, all compositionalpercentages are by weight of the total composition, unless otherwisespecified. As used herein, the word “include,” and its variants, isintended to be non-limiting, such that recitation of items in a list isnot to the exclusion of other like items that may also be useful in thematerials, compositions, devices, and methods of this technology.Similarly, the terms “can” and “may” and their variants are intended tobe non-limiting, such that recitation that an embodiment can or maycomprise certain elements or features does not exclude other embodimentsof the present invention that do not contain those elements or features.

Although the terms “first” and “second” may be used herein to describevarious features/elements (including steps), these features/elementsshould not be limited by these terms, unless the context indicatesotherwise. These terms may be used to distinguish one feature/elementfrom another feature/element. Thus, a first feature/element discussedbelow could be termed a second feature/element, and similarly, a secondfeature/element discussed below could be termed a first feature/elementwithout departing from the teachings of the present invention.

Spatially relative terms, such as “under”, “below”, “lower”, “over”,“upper”, “in front of” or “behind” and the like, may be used herein forease of description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. It willbe understood that the spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. For example, if adevice in the figures is inverted, elements described as “under” or“beneath” other elements or features would then be oriented “over” theother elements or features. Thus, the exemplary term “under” canencompass both an orientation of over and under. The device may beotherwise oriented (rotated 90 degrees or at other orientations) and thespatially relative descriptors used herein interpreted accordingly.Similarly, the terms “upwardly”, “downwardly”, “vertical”, “horizontal”and the like are used herein for the purpose of explanation only unlessspecifically indicated otherwise.

When a feature or element is herein referred to as being “on” anotherfeature or element, it can be directly on the other feature or elementor intervening features and/or elements may also be present. Incontrast, when a feature or element is referred to as being “directlyon” another feature or element, there are no intervening features orelements present. It will also be understood that, when a feature orelement is referred to as being “connected”, “attached” or “coupled” toanother feature or element, it can be directly connected, attached orcoupled to the other feature or element or intervening features orelements may be present. In contrast, when a feature or element isreferred to as being “directly connected”, “directly attached” or“directly coupled” to another feature or element, there are nointervening features or elements present. Although described or shownwith respect to one embodiment, the features and elements so describedor shown can apply to other embodiments. It will also be appreciated bythose of skill in the art that references to a structure or feature thatis disposed “adjacent” another feature may have portions that overlap orunderlie the adjacent feature.

The description and specific examples, while indicating embodiments ofthe technology, are intended for purposes of illustration only and arenot intended to limit the scope of the technology. Moreover, recitationof multiple embodiments having stated features is not intended toexclude other embodiments having additional features, or otherembodiments incorporating different combinations of the stated features.Specific examples are provided for illustrative purposes of how to makeand use the compositions and methods of this technology and, unlessexplicitly stated otherwise, are not intended to be a representationthat given embodiments of this technology have, or have not, been madeor tested.

All publications and patent applications mentioned in this specificationare herein incorporated by reference in their entirety to the sameextent as if each individual publication or patent application wasspecifically and individually indicated to be incorporated by reference,especially referenced is disclosure appearing in the same sentence,paragraph, page or section of the specification in which theincorporation by reference appears.

The citation of references herein does not constitute an admission thatthose references are prior art or have any relevance to thepatentability of the technology disclosed herein. Any discussion of thecontent of references cited is intended merely to provide a generalsummary of assertions made by the authors of the references, and doesnot constitute an admission as to the accuracy of the content of suchreferences.

The invention claimed is:
 1. A method for making nanocrystallinecellulose (“NCC”) comprising: contacting frozen concentrated sulfuricacid with microcrystalline cellulose (“MCC”) to form a mixture, andholding the mixture at a hydrolysis temperature ranging from about 10°C. to 15° C. for a time sufficient to form a cellulosic paste containinghydrolyzed MCC, diluting the cellulosic paste containing hydrolyzed MCCin a mixture comprising liquid water and water ice to precipitate NCC,and separating the precipitated NCC, thus making NCC, wherein the frozenconcentrated sulfuric acid has a concentration of at least 95 mass %. 2.The method of claim 1, wherein the MCC is in the form of precooledcellulosic fibers at a temperature of less than 25° C.
 3. The method ofclaim 1, wherein the concentrated sulfuric acid has a concentration ofabout 98.06 mass % and the cellulosic paste is white.
 4. The method ofclaim 1, wherein contacting and diluting occurs at a temperature rangingfrom 10° C. to 15° C.
 5. The method of claim 1, wherein the contactingoccurs at a wt/wt ratio of sulfuric acid to MCC of 2:1 to 1:2.
 6. Themethod of claim 1, wherein the diluting occurs at a ratio of liquidwater and water ice to MCC of 2:1 to 1:2 (wt/wt).
 7. The method of claim1, wherein the separating is performed by filtering.
 8. The method ofclaim 1, wherein the separating is performed by filtering, wherein thefiltering is performed at a temperature ranging from 0° C. to 15° C. 9.The method of claim 1, further comprising washing the separated NCC withwater to increase the pH of the NCC.
 10. The method of claim 1, furthercomprising washing the separated NCC with water to increase the pH ofthe NCC to pH 6.5 to pH 7.5.
 11. The method of claim 1, wherein theseparated NCC is washed with water to increase the pH of the NCC to pH6.5 to pH 7.5 and further comprising drying the washed NCC.
 12. Themethod of claim 1, wherein the MCC is contacted directly with the frozenconcentrated sulfuric acid without addition of water or pre-wetting ofthe MCC and wherein the NCC is produced without sonication or ultrasonicprocessing and with out centrifugation.
 13. The method of claim 1, whichproduces in 60 minutes or less a yield of NCC of at least about 50 wt %based on the weight of the MCC.
 14. A composition comprising MCC, frozenconcentrated sulfuric acid, and water ice: wherein the concentratedsulfuric acid has a concentration of at least 95 mass %.